Variations in cylinder compression ratios may arise in engines due to the manufacturing tolerances of different components as well as stack-up tolerances in groups of components. For instance, the tolerances in components influencing piston squish height and bowl volume can cause variations in cylinder compression in multi-cylinder engines. Often the compression ratio can vary cylinder to cylinder by +/−1.0%, for instance, which can cause variations in the power produced by each cylinder. Consequently, the power and fuel consumption of the engine may be reduced and the drivability of a vehicle in which the engine resides may be negatively affected. These problems may be particularly prevalent in compression ignition engines. However, variations in compressions ratios can also have negative impacts on spark-ignition engines.
One example approach shown by Cannata, in U.S. Pat. No. 7,827,943 B2, includes a system that varies a compression ratio in a cylinder via a mechanical assembly that adjusts the position where the connecting rod and the piston are attached. However, Cannata's system achieves compression ratio adaptability at the expense of engine reliability. For example, Cannata's mechanical compression ratio adjustment system may be prone to malfunction and failure due to the complexity of the mechanical components used to adjust the compression ratios.
The inventors have recognized the aforementioned problems with previous engines and facing these challenges developed a method for operation of an engine, in one example, to address the problems. The method includes determining a variation between compression ratios in a first combustion chamber and a second combustion chamber and operating a piston heating system to apply a targeted amount of heat to a first piston assembly based on the variation between the compression ratios, the first piston assembly including a first piston positioned within the first combustion chamber. In this way, the compression ratio of each cylinder may be adjusted to reduce variations between the compression ratios in the engine and stabilize the amount of torque produced by the cylinders, if desired, through a robust and reliable compression ratio adjustment system. Consequently, engine efficiency can be increased while reducing noise, vibration, and harshness (NVH) caused by the torque imbalance. Such compression ratio adjustment is also carried out using a dependable system that is not prone to malfunction. As a result, the drivability as well as the reliability of the vehicle may be increased, thereby increasing customer satisfaction.
In one example, operating the piston heating system may include activating a heater coupled to a lubrication line, the lubrication line including a nozzle directing lubricant to a first piston rod coupled to the first piston and a crankshaft during engine operation. In this way, a piston assembly heater can be incorporated into a lubrication system to induce compression ratio adjustment in an efficient and reliable manner.
In another example, the amount of heat delivered to combustion chambers in the engine may be varied based on engine load. In such an example, during low load conditions (e.g., when the engine load is below a predetermined threshold value) piston assembly heaters coupled to the first and second combustion chambers may be activated or operated to increase an amount of heat delivered to the combustion chambers to increase the compression ratios in the combustion chambers. Consequently, the piston heating system can also be used to increase combustion efficiency in the engine during low load conditions, for instance.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.